(1) Background of the Invention
The present invention relates to a technique on a fail-safe control when a failure of any one or more of frictional engaging elements in a multiple-speed (or planetary gear type stepped) automatic transmission.
(2) Description of Related Art
A Japanese Patent Application Publication (tokkai) 2005-155719 published on Jun. 16, 2005 (which corresponds to a U.S. Pat. No. 7,128,683 issued on Oct. 31, 2006) exemplifies a previously proposed multiple-speed (or planetary gear type stepped) automatic transmission which is equipped with four couples of planetary gears and seven couples of frictional engaging elements and which is capable of switching gear shift stages of forward seven speeds (forward seven gear ratios) and one reverse speed (one reverse gear ratio).